JVM专题之内存模型以及如何判定对象已死问题
体验与验证
2.4.5.1 使用visualvm
**visualgc插件下载链接 ：https://visualvm.github.io/pluginscenters.html
https://visualvm.github.io/pluginscenters.html
**选择对应JDK版本链接--->Tools--->Visual GC**
2.4.5.2 堆内存溢出
* **代码**
java
@RestController
public class HeapController {
List<Person> list=new ArrayList<Person>();
@GetMapping("/heap")
public String heap(){
while(true){
list.add(new Person());
}
}
}
```
记得设置参数比如-Xmx20M -Xms20M**
* **运行结果**
`访问`：http://localhost:8080/heap http://localhost:8080/heap
```
Exception in thread "http-nio-8080-exec-2" java.lang.OutOfMemoryError: GC overhead limit exceeded
```
2.4.5.3 方法区内存溢出
> **比如向方法区中添加Class的信息**
* **asm依赖和Class代码**
```xml
<dependency>
<groupId>asm</groupId>
<artifactId>asm</artifactId>
<version>3.3.1</version>
</dependency>
```
```java
public class MyMetaspace extends ClassLoader {
public static List<Class<?>> createClasses() {
List<Class<?>> classes = new ArrayList<Class<?>>();
for (int i = 0; i < 10000000; ++i) {
ClassWriter cw = new ClassWriter(0);
cw.visit(Opcodes.V1_1, Opcodes.ACC_PUBLIC, "Class" + i, null,
"java/lang/Object", null);
MethodVisitor mw = cw.visitMethod(Opcodes.ACC_PUBLIC, "<init>",
"()V", null, null);
mw.visitVarInsn(Opcodes.ALOAD, 0);
mw.visitMethodInsn(Opcodes.INVOKESPECIAL, "java/lang/Object",
"<init>", "()V");
mw.visitInsn(Opcodes.RETURN);
mw.visitMaxs(1, 1);
mw.visitEnd();
Metaspace test = new Metaspace();
byte[] code = cw.toByteArray();
Class<?> exampleClass = test.defineClass("Class" + i, code, 0, code.length);
classes.add(exampleClass);
}
return classes;
}
}
```
* **代码**
```java
@RestController
public class